Hot casting repair mix

ABSTRACT

An object is to provide a nonaqueous hot casting repair mix which, while enjoying simple and convenient installation, can substantially reduce hardening time after installation. The hot casting repair mix according to the invention is characterized by containing 5 to 30% by weight of a binder capable of forming a carbon bond in hot condition and 1 to less than 5% by weight of an iron powder and the balance consisting of a refractory aggregate.

TECHNICAL FIELD

The present invention relates to a hot casting repair mix for repairingvarious refining furnace, vessels, and the like in hot condition.

BACKGROUND ART

As a hot repairing method of molten metal vessels such as steelconverters and ladles, a method of charging a powdery repairing materialinto the furnace and baking the material is widely used sincetransportation and storage of the material are easy and additionallyinstallation is simple and convenient such that a prior kneading step,e.g., included in cast repairing is unnecessary and the material ischarged into the furnace and baked by remaining heat of the furnace. Thepowdery hot casting repair mixes are roughly classified into aqueous oneand nonaqueous one. As the aqueous material, for example, hot castingrepair mixes which use phosphate salts or silicate salts containingwater of crystallization are disclosed in Patent Document 1.

The nonaqueous hot casting repair mix using tar, pitch or the like isknown to have a good durability as compared with the aqueous hot castingrepair mix but the former material has a drawback that a long hardeningtime is required. In Patent Document 2, addition of Mg powder isdisclosed as a method for reducing the hardening time. However, thereremain problems that the Mg powder not only is expensive and lowerseconomical efficiency but also has a high risk of dust explosion andthus the greatest care is necessary for handling of raw materials duringproduction.

On the other hand, Patent Document 3 discloses addition of an ironpowder and an Al powder as a technology for improving a nonaqueous hotcasting repair mix. During baking, the iron powder precipitates insidethe material and has an action of heat absorption from an adheringsurface, so that the powder improves adhesiveness of the hot castingrepair mix. However, actually, even when the material adheres once bythe cooling effect during baking, since the iron powder is present as afilm of molten iron between the hot casting repair mix and furnace wall(adhering surface), adhesion strength is impaired and rather exfoliationtends to occur, so that improvement in durability has not been achieved.

Patent Document 1: Japanese Patent Application Raid-Open: JP-A-2-26874Patent Document 2: Japanese Patent Application Raid-Open: JP-A-11-240771Patent Document 3: Japanese Patent Application Raid-Open: JP-A-11-278948DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

Many of recent molten metal vessels such as steel converters and ladlesare those where a carbon-based refractory is used as a liner. Form theviewpoint of adhesiveness to the mother material, a nonaqueous materialcapable of forming a carbon bond upon hot work is desired in the hotrepairing. However, a powdery nonaqueous hot casting repair mix enableseasy installation but has a drawback that the hardening time aftercharging is long and hence there is a problem that the material cannotbe used in the case where a long repairing time is not allowed.

Means for Solving the Problems

The invention provides a powdery nonaqueous hot casting repair mixwhich, while enjoying simple and convenient installation, cansubstantially reduce the hardening time after installation and isexcellent in economical efficiency and durability.

Namely, it is a hot casting repair mix comprising 5 to 30% by weight ofa binder capable of forming a carbon bond in hot condition and 1 to lessthan 5% by weight of an iron powder and the balance consisting of arefractory aggregate.

Furthermore, in the present invention, a better effect is obtained inthe case where a fluidization promoter is contained in an amount of 0.1to 1% by weight relative to 1% by weight of the binder capable offorming a carbon bond in hot condition and the total amount of thebinder capable of forming a carbon bond in hot condition and thefluidization promoter is 5 to 30% by weight and an iron powder iscontained in an amount of 1 to less than 5% by weight and the balanceconsisting of a refractory aggregate.

Namely, for the purpose of imparting fluidization, it is preferred toadd a fluidization promoter within a range where the sedimentation ofthe iron powder is not facilitated and the effect is not inhibited.

The furnace wall of the molten metal vessel to be repaired is so hot asat least 700° C. or higher. When the hot casting repair mix according tothe present invention is charged into the furnace, a powdery particulatebinder is melted by remaining heat of the furnace and the wholerepairing material becomes in a fluidized state, so that it fills intodetails of places to be repaired and at the same time a refractorymaterial is closely filled. Then, the hot casting repair mix forms acarbon bond after hardened by the action of the binder.

Since the hot casting repair mix of the present invention has animproved thermal conductivity of the material owing to the addition ofthe iron powder, elevation of the material temperature is rapid andcarbonation of the binder is promoted during fluidization and heatreception in hot condition, so that the hardening time is substantiallyreduced. The iron powder precipitates by gravity separation from therefractory aggregate during the fluidization but it becomes possible tosuppress an adverse effect on the adhering surface by limiting theamount thereof to be added.

ADVANTAGE OF THE INVENTION

Since the hot casting repair mix of the present invention caneffectively transfer furnace heat to the material during baking, thehardening time can be reduced. Moreover, since the adhesion strength isnot impaired during hot working, exfoliation hardly occurs and thus thematerial is excellent in durability. The hot casting repair mix of thepresent invention remarkably contributes to improvement in working ratioand life of the furnaces such as molten metal vessels owing to theeconomical efficiency and an excellent repairing effect.

BEST MODE FOR CARRYING OUT THE INVENTION

The refractory aggregate for use in the present invention is notparticularly limited and suitable one adapted to the mother materialused at the place to be repaired can be employed. For example, therefractory aggregate is one or more of acidic oxides such as silica andzircon; neutral oxides such as alumina and chromia; basic oxides such asmagnesia, calcia and dolomite; non-oxides such as carbonaceousmaterials, silicon carbide and silicon nitride; various kinds of brickscraps; and the like. It is preferable for these refractory aggregatesto suitably adjust the grain size to coarse grains, medium grains, andfine grains so that the structure of the hot casting repair mix becomesa closely packed structure.

The iron powder for use in the present invention includes iron alloysbut the purity of Fe is not particularly limited and inexpensive one ispreferable from economical viewpoints. The amount of the iron powder tobe used is 1 to less than 5% by weight relative to 100% by weight of thehot casting repair mix. When the amount is less than 1% by weight, theeffect of the present invention (improvement in thermal conductivity ofthe material) is not sufficiently obtained and thus the hardening timeis not reduced. Moreover, when the amount is 5% by weight or more, theiron powder precipitates on the repairing surface (adhering surface)during fluidization, the film of molten iron formed on the adheringsurface at the operation of the furnace after hot casting repairingincreases, and exfoliation tends to occur, so that the case is notpreferable.

Furthermore, the grain size of the iron powder for use in the presentinvention is preferably fine and coarse grains are not preferable sincethe iron powder tends to precipitate during fluidization. Whenavailability in the market is considered, a maximum grain size of 1.5 mmor less is preferable. A lower limit of the grain size is notparticularly defined so far as it is fine within an inexpensivelyavailable range. Incidentally, the use of aluminum known as anantioxidant, copper having a high thermal conductivity and the like canalso bring about expectation of the effect of improving thermalconductivity of the material but the use is not preferable since theyare expensive and thus lower economical efficiency.

As the binder capable of forming a carbon bond during hot work, apowdery particulate pitch or phenol resin used as a usual organic bindercan be employed. The amount of the binder capable of forming a carbonbond to be used is 5 to 30% by weight relative to 100% by weight of thehot casting repair mix. When the amount is less than 5% by weight, thecarbon bond is not sufficiently formed and an executed body inferior instrength and adhesiveness is obtained and when the amount exceeds 30% byweight, an executed body having a large porosity is obtained and thusanticorrosive properties decrease.

The fluidization promoter is used for promoting fluidization by meltsoftening of the binder and imparting wide repairing area andheat-receiving area to the hot casting repair mix. One or two or moreselected from p-alkylphenols, lactams, bisphenol, diphenyl,diphenylamine, paraffin, wax and the like can be used.

In the case of using the fluidization promoter, the total amount of thebinder capable of forming a carbon bond in hot condition and thefluidization promoter is 5 to 30% by weight and the fluidizationpromoter is used in an amount of 0.1 to 1% by weight, preferably 0.1 to0.6% by weight relative to 1% by weight of the binder capable of forminga carbon bond. When the amount is less than 0.1% by weight, thefluidization promoting effect is not obtained and when the amountexceeds 1% by weight, the viscosity of the hot casting repair mix tendsto decrease and the iron powder precipitates on the repairing surface(adhering surface), so that the cases are not preferable.

EXAMPLES

The following will describe the invention specifically with reference toinventive products, which are Examples of the invention, together withcomparative products but the invention is not limited by the followinginventive products.

Table 1 shows Examples and Comparative Examples regarding the hotcasting repair mix of the present invention.

Evaluation of hot flowability: 800 g of a formulation shown in Table 1was charged onto a castable plate in a furnace kept at 1000° C.; afterextinction, the castable plate was taken out of the furnace and anaverage value of the diameter of the resulting spread hot casting repairmix was measured as hot flowability.

Evaluation of hardening time: with regard to the hardening time, aring-shaped metal flame having an inner diameter of 53 mm and a heightof 40 mm was placed on a magnesia brick kept at 1000° C., 200 g of asample was charged thereon, and the time required for hardening thewhole was measured. After hardening of the sample, adhesive strength wasimmediately measured by means of a shear adhesive strength-measuringmachine.

Evaluation of apparent porosity: 1 kg of a sample was charged into acircle surrounded by magnesia bricks in a furnace kept at 1000° C. and,after hardening, apparent porosity of the repaired body was alsomeasured.

Evaluation of actual furnace ch number: for an actual furnace test, 600kg of a hot casting repair mix was used in hot repairing of a 300 tsteel converter lined with MgO-C brick and the number of charges whenthe remaining area of the hot casting repair mix became 20% or less ofthe area immediately after repairing was evaluated as durability.

Examples of the present invention had a short hardening time and alsoshowed a good durability in the actual furnace test. Since adhesivestrength was low and apparent porosity of the repaired body was large inComparative Examples 1 and 2, the actual furnace test was not carriedout. In Comparative Examples 3 and 4, the hardening time was short butdurability on the actual furnace test was no good.

TABLE 1 Example Comparative Example 1 2 3 4 5 1 2 3 4 RefractoryMagnesia aggregate 42 40 40 40 35 50 29.5 32 38 aggregate 8 to 1 mm (%by weight) Magnesia aggregate 41 38 38 43 33 46 25 34 35 1 mm or lessBinder Pitch powder 8 15 20 10 25 4 20 18 (% by weight) (softening point110° C.) Thermoplastic powdery 5 20 phenol resin Fluidization BisphenolA 3 3 1 promoter p-Alkylphenol 5 25 (% by weight) (melting point 84° C.)Iron powder Iron powder 15 7 (% by weight) average particle size 3 mmIron powder 4 2 4 0.5 average particle size 1 mm Iron powder 4 2 averageparticle size 0.5 mm Test result Hot flowability (mm) 215 235 252 230263 142 295 240 260 Hardening time (min) 3 3 4 3 5 3 15 6 6 Adhesivestrength (MPa) 3.8 4.6 5.8 4.2 6.2 0.2 0.9 3.6 2.0 Apparent porosity (%)23.5 25.4 26.3 24.0 29.2 33.8 38.4 25.6 24.5 Actual furnace durable ch13 15 18 14 16 — — 3 6 number

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

The present application is based on Japanese Patent Application No.2007-133444 filed on May 18, 2007, and the contents are incorporatedherein by reference.

Also, all the references are incorporated as a whole.

1. A hot casting repair mix comprising 5 to 30% by weight of a bindercapable of forming a carbon bond in hot condition and 1 to less than 5%by weight of an iron powder and the balance consisting of a refractoryaggregate.
 2. The hot casting repair mix according to claim 1, wherein afluidization promoter is used in an amount of 0.1 to 1% by weightrelative to 1% by weight of the binder capable of forming a carbon bondin hot condition and the total amount of the binder capable of forming acarbon bond in hot condition and the fluidization promoter is 5 to 30%by weight and an iron powder is contained in an amount of 1 to less than5% by weight and the balance consisting of a refractory aggregate.